International patent application WO 2004/052253 A1 describes an excimer laser unit and a corresponding control method for performing a corneal ablation to reduce presbyopia. Here, the excimer laser unit is controlled in such a way that, through the ablation of the cornea, a slightly positive fourth-order spherical aberration (Z(4.0)) is created in the cornea. The loss of the power of accommodation of the eye caused by presbyopia is at least partially compensated for by the increase in the spherical aberration of the eye thus achieved. By incorporating a positive fourth-order spherical aberration, a considerable improvement in near vision can be achieved, especially in the case of presbyopia.
However, it has been found that, by incorporating a spherical aberration of the type described in WO 2004/052253 A1, the base refraction of the eye is changed. This results in a deterioration of the distance vision or far vision. Consequently, with the known method, creating a fourth-order aberration achieves an improvement of the near vision in cases of presbyopia, but this comes “at the expense of” the distance vision.